1. Field of the Invention
This invention relates to plasmids being capable of being replicated in thermophilic bacteria and in particular plasmids being capable of stably being replicated in grampositive thermophilic bacteria which grow at high temperature.
2. Description of the Related Art
As for plasmids which are capable of being replicated in thermophilic bacteria, particularly thermophilic bacteria of genus Bacillus, some plasmids such as pUB110, pIH41 and the like have been reported. However, these plasmids which were introduced in a host have been more frequently lost from the host when the host with the plasmids was incubated at a temperature of 60.degree. C. or more without applying selection pressure due to addition of antibiotic substances (for example, "Gene Technology" edited by T. Andou et al., pp. 134-167, Kyouritu Shuppan K. K., 1987), the disclosure of which is hereby incorporated by reference herein.
The above-mentioned plasmids encode resistance factors against antibiotic substances such as kanamycin or the like. For this reason, by incubating the plasmid-bearing bacterium in a culture medium containing the corresponding antibiotic substance, it is possible to selectively kill the host from which the plasmids were lost and to grow only the plasmid-bearing host, whereby the loss of the plasmids can be apparently prevented. However, in addition to the cost for the antibiotic substance usage, treatment of the residual antibiotic substance in the culture medium after incubation is very expensive. Thus, mass incubation of the plasmid-bearing bacteria requires great deal of expense.